The present invention relates to an improved in-ground/in-water heat exchange means for use in association with any heat pump heating/cooling system utilizing in-ground and/or in-water heat exchange elements as a primary or supplemental source of heat transfer.
Ground source/water source heat exchange systems typically utilize liquid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged tubing.
Water-source heat pump heating/cooling systems typically circulate water, or water with anti-freeze, in plastic underground geothermal tubing so as to transfer heat to or from the ground, with a second heat exchange step utilizing a refrigerant to transfer heat to or from the water, and with a third heat exchange step utilizing a compressor and an electric fan to transfer heat to or from the refrigerant to heat or cool interior air space. Further, water-source heating/cooling systems typically utilize closed-loop or open-loop plastic tubing.
Closed-loop systems, often referred to as ground loop heat pumps, typically consist of a supply and return, ¾ inch to 2 inch diameter, plastic tube, joined at the extreme ends via an elbow, or similar, connection. The plastic tubing is typically of equal diameter, wall thickness, and composition, in both the supply and return lines. The water is circulated within the plastic tubing by means of a water pump. In the summer, interior space heat is collected by an a commonly understood interior compressor and air heat exchanger system, or air handler, and is rejected and transferred into the water line via a refrigerant line to water line heat exchanger. In a similar manner in the winter, heat is extracted from the water line and transferred to the interior conditioned air space via the refrigerant liquid within the refrigerant line being circulated in a reverse direction. Many such systems are designed to operate with water temperatures ranges of about a 10 degree Fahrenheit (“F”) water temperature differential between the water entering and exiting the heat exchange unit's copper refrigerant transport tubing. Water temperatures are often designed to operate in the 40 to 60 degree F. range in the summer and in the 25 to 45 degree F. range in the winter with anti-freeze added to the water. If a closed-loop, 1.5 inch diameter, plastic water conducting tubing is installed in a horizontal fashion about 5 or 6 feet deep, in 55 degree F. earth, about 200 to 300 linear feet per ton of system capacity may be necessarily excavated. If the same closed-loop plastic water conducting tubing is installed in a vertical borehole in 55 degree F. earth, about 150 to 200 feet per ton of system capacity may be necessarily drilled. Requisite distances are longer for horizontal systems because near-surface temperature fluctuations are greater. However, trenching costs are usually less than drilling expenses. In the horizontal style installation, the plastic tubing loop is typically backfilled with earth. In the vertical style installation, the plastic tubing loop inserted into the typical 5 to 6 inch diameter borehole is generally backfilled with a thermally conductive grout. In either the horizontal or the vertical style installation, a water pump is required to circulate the water through the tubing lines, which are generally of equal diameter in both the supply and return segments.
Open-loop systems, often referred to as ground water heat pumps, typically exchange heat to and from interior conditioned air in the same manner as a closed-loop system, but the water circulation segment differs. In an open-loop system, water is pumped from a supply source, such as a well, river, or lake, is run through the water to refrigerant heat exchanger, and is then rejected back into a well, river, or lake. While open-loop systems can significantly reduce plastic tubing excavation or drilling requirements on a system capacity tonnage basis, if an adequate water supply is available, these systems pose a potential environmental threat since bacteria in the surface water transport tubing can be transferred to, and can infect, the water which is being rejected back into the public water supply.
Direct Expansion (“DX”) ground source heat exchange systems typically circulate a refrigerant fluid, such as one of R-22 and R-410A, in copper underground or underwater geothermal tubing to transfer heat to or from the ground or water, and only require a secondary heat exchange step to transfer heat to or from the interior air space by means of an electric fan. In DX systems, the exterior heat exchange copper refrigerant tubing is placed directly in the geothermal soil and/or water. Historically, due to compressor operational limitations encountered with traditional DX designs installed at depths beyond 50 to 100 feet, most reverse-cycle DX systems, which operate in both the heating and the cooling modes, have been installed with an array of horizontal heat exchange tubes about 5 feet deep, or in vertical boreholes less than 100 feet deep. These prior limitations can be overcome via utilization of a supplemental refrigerant fluid pump, as disclosed in U.S. Utility patent application Ser. No. 10/073,513, by Wiggs.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements are taught in U.S. Pat. No. 5,623,986 to Wiggs, in U.S. Pat. No. 5,816,314 to Wiggs, et al., and in U.S. Pat. No. 5,946,928 to Wiggs, the disclosures of which are incorporated herein by reference. These designs basically teach the utilization of a spiraled fluid supply line subjected to naturally surrounding geothermal temperatures, with a fully insulated fluid return line, as well as improved subterranean heat transfer tubing and system component designs.
Other predecessor vertically oriented geothermal heat exchange designs are disclosed by U.S. Pat. No. 5,461,876 to Dressler, and by U.S. Pat. No. 4,741,388 to Kuriowa. Dressler's '876 patent teaches the utilization of an in-ground spiraled fluid supply line, but neglects to insulate the fluid return line, thereby subjecting the heat gained or lost by the circulating fluid to a “short-circuiting” effect as the return line comes in close contact with the warmest or coldest portion of the supply line. Kuriowa's preceding '388 patent is virtually identical to Dressler's subsequent claim, but better, because Kuriowa insulates a portion of the return line, via surrounding it with insulation, thereby reducing the “short-circuiting” effect. Dressler's '876 patent also discloses the alternative use of a pair of concentric tubes, with one tube being within the core of the other, with the inner tube surrounded by insulation or a vacuum. While this multiple concentric tube design reduces the “short-circuiting” effect, it is practically difficult to build and could be functionally cost-prohibitive.
The problem encountered with insulating the heat transfer return line, by means of fully surrounding a portion of same with insulation as per Kuriowa, or by means of a fully insulated concentric tube within a tube as per Dressler, or by means of a fully insulated return line as per Wiggs' predecessor designs, is that the fully insulated portion of the return line is not exposed to naturally occurring geothermal temperatures, and is therefore a costly necessary underground/underwater system component which is not capable of being utilized for geothermal heat transfer purposes. While the utilization of such fully insulated costly components is an improvement over prior totally un-insulated geothermal heat transfer line designs subject to a “short-circuiting” of the maximum heat gain/loss potential, a design which insulates the supply line from the return line and still permits both lines to retain natural geothermal heat exchange exposure would be preferable, as disclosed in U.S. Utility patent application Ser. No. 10/127,517 by Wiggs. Further, of course, even in horizontal and vertical closed-loop water-source heat pump systems, this “short-circuiting” effect, caused by the supply and return water transfer lines being in close proximity to one another, is a problem which deters from operational system efficiencies.
An additional problem encountered with traditional closed-loop water-source systems is the fact that, traditionally, ¾ inch to 2 inch diameter plastic water transfer tubing is utilized, so as to reduce plastic pipe costs and excavation/drilling expenses. However, as a general principle, smaller pipe sizes have greater friction efficiency losses, which result in increased requisite pumping energy.
In the early 1990s, Wiggs developed the proposition of excavating a large surface, and near-surface, area of land for the placement of a sealed container, filled with a heat conductive liquid, such as water or water and anti-freeze, and then permanently placing the exterior heat exchange tubes of a direct expansion system into the liquid-filled container. However, after a more detailed review and confidential discussion with others, it was determined that the cost, as well as the requisite surface land area requirements, involved were not likely to be advantageous over a conventional direct expansion exterior heat exchange tube installation design, so the proposition was abandoned by Wiggs. Further, such an installation would still be affected by near-surface temperature fluctuations in both the summer and the winter, and would still be subjected to “short circuiting” efficiency disadvantages encountered by a mixture of heated and cooled container liquid. The present invention, however, is superior to Wiggs' former proposition in that via the subject invention, deep sub-surface temperatures are accessed which are relatively stable year round; surface area requirements to install the system are minimal, avoiding the necessity of tearing up a yard or a pavement area; and the otherwise necessary extensive excavation and soil removal costs are replaced by a simple drilling expense. Further, and importantly, the “short circuiting” disadvantages are avoided.
Finally, while discussions have been entertained regarding the desirability of incorporating solar heating benefits into a geothermal heat pump heating system, as well as incorporating evaporative cooling benefits into a geothermal cooling system, there have been practical obstacles, such as potential extreme system operational pressure differentials, flash gas problems, system short-cycling, and energy storage issues. A supplemental solar heating system designed to overcome these obstacles, while augmenting a geothermal heat pump heating system, would be preferable.
Although potentially unnecessary in a sub-surface application where the sub-surface conditions include a substantial amount of natural water convection, such as in a lake, ocean, or aquifer, where the Thermally Exposed Centrally Insulated Geothermal Heat Exchange Unit disclosed by Wiggs in U.S. Utility patent application Ser. No. 10/127,517 would be appropriate, a system design for geothermal direct expansion heat pumps, and/or for geothermal water-source heat pumps, which better avoided “short-circuiting” problems, which decreased friction efficiency losses, and which enabled solar heating and/or evaporative cooling supplements to be effectively utilized, with minimal additional costs, in subterranean soil and/or rock and/or stagnate water conditions, would be preferable. Such a preferable system would also be utilized in conditions containing a substantial amount of natural water convection where it would be useful to isolate the liquid coming into direct contact with copper refrigerant tubing from the surrounding natural water conditions, such as when the natural surrounding water conditions contain significant amounts of sulfur, acid, chlorine, or other substance potentially harmful to copper refrigerant tubing.